{circle around (1)} In a conventional high pressure fuel supply pump, for example, as shown in Japanese Patent No. 2690734Specification, fuel is supplied from a tank to a high pressure pump by a low pressure pump to increase its pressure to high, and is supplied to a common rail. Within the high pressure pump, an intake passage and a discharge passage are communicated with an upper end surface of a pressurizing chamber and an intermediate side wall of the pressurizing chamber, respectively.
Further, in the other conventional high pressure fuel supply pump, for example, as shown in Japanese Patent Application Laid-Open No. Hei10-318091 Publication, an intake passage and a discharge passage are communicated with an intermediate side wall or an upper end surface of a pressurizing chamber and an upper end surface of the pressurizing chamber, respectively.
Incidentally, when the engine is first started, or restarted after stoppage for a long period, vapor of air or fuel is present within a fuel pipe. Therefore, immediately after start, the pressure increasing characteristic of the high pressure pump is apt to be deteriorated. To prevent this, it is necessary to rapidly discharge air or fuel vapor within the pressurizing chamber of the high pressure pump to thereby secure the pressure increasing characteristic of the high pressure pump, and to rapidly supply fuel into the common rail by a low pressure pump of large discharge capacity.
However, in the high pressure fuel supply pump described in Japanese Patent No. 2690734 Specification, an intake passage and a discharge passage are provided on an upper end surface of a pressurizing chamber and an intermediate side wall of the pressurizing chamber, respectively, thus posing a problem in that in the intake stroke, vapor or the like is hard to be discharged on the intake passage side due to the intake fuel, and in the discharge stroke, the vapor or the like is apt to remain within the pressurizing chamber above the discharge passage, thereby lowering the supply property of fuel.
Also in the constitution described in FIG. 5 of Japanese Patent Application Laid-Open No. Hei10-318091 Publication, a discharge passage within the high pressure pump is provided in an upper end of a pressurizing chamber, and therefore, vapor within the pressurizing chamber is apt to be discharged. However, both the above-described prior arts have a problem in that since fuel fed from the low pressure pump is communicated with the pressurizing chamber which changes in volume due to piston motion within the high pressure pump, even if an attempt is made to supply fuel to the common rail by the low pressure pump immediately after the engine starts, the piston motion within the pressurizing chamber makes resistance to delay a supply of fuel.
Further, in the conventional constitution described in FIG. 1 of Japanese Patent Application Laid-Open No. Hei10-318091 Publication, since an upper flat surface of a cylinder fixing portion is compressed and fitted, fuel flows into the outer periphery of a delivery valve passing through the outer circumference of a cylinder when the intake passage is communicated with the intermediate side wall of the pressurizing chamber, because of which, an O-ring is provided for sealing from outside. However, this poses a problem in that when an O-ring is formed from an elastic member, it moves due to the pressure variation in the pressuring chamber, and therefore, pressure rising of the pressurizing chamber reduces, or rubbing wear or rupture of the O-ring occurs.
{circle around (2)} Further, with respect to a seal mechanism against a leakage of high pressure fuel, in the conventional high pressure fuel supply pump, fuel in the pressurizing chamber is increased to high pressure by reciprocating movement of a plunger. Here, since fuel pressure pressurized is considerably high pressure, fuel possibly leaks out of a clearance between the plunger and the cylinder.
In view of the foregoing, in the conventional high pressure fuel supply pump, a seal material of an elastic member is disposed on the end of a sliding portion of a plunger, as described in Japanese Patent Application Laid-Open No. Hei 10-318068 Publication and Japanese Patent Application Laid-Open No. Hei8-368370 Publication, to prevent a leakage of fuel. On the fuel chamber side of the seal material is provided with a passage communicated with a fuel tank which is substantially at atmospheric pressure. Further, a sliding portion of the plunger is provided therein with a fuel reservoir leading to a fuel intake port which is a low pressure portion. By the provision of these constitutions noted above, when one end of the seal material is in contact with the atmospheric pressure, the other end is also communicated with the fuel tank to be substantially atmospheric pressure so as not to apply high pressure of the pressurizing chamber onto the seal material directly, thus preventing a leakage of fuel from the seal material.
However, the high pressure fuel supply pump described in FIG. 1 of Japanese Patent Application Laid-Open No. Hei 10-318068 Publication poses a problem in that since the distance from the fuel reservoir (a pulsation reducing space in FIG. 1) in communication with the low pressure fuel chamber to the sliding end of the plunger is short, when the seal material is broken or fallen off, a large quantity of fuel possibly flows outside from a clearance of the plunger sliding portion.
On the other hand, in the high pressure fuel supply pump described in FIG. 1 of Japanese Patent Application Laid-Open No. Hei 8-68370 Publication, since the distance from the fuel reservoir (a sliding hole 11a of a cylinder 11 in FIG. 1) in communication with the low pressure fuel chamber to the sliding end of the plunger is long, it is possible to make small the quantity of fuel which flows out when the seal material is broken or fallen off. However, since the sliding distance of the plunger from the pressurizing chamber to the fuel reservoir cannot be made long, thus posing a problem in that when pressurized, fuel leaks into the low pressure portion from a clearance of the sliding portion of the plunger to deteriorate the discharge efficiency.
Further, in the high pressure fuel supply pump described in FIG. 1 of Japanese Patent Application Laid-Open No. Hei 8-68370 Publication, the distance from the pressurizing chamber to the fuel reservoir is prolonged to thereby enable prevention of a leakage of fuel, but it is necessary, to this end, to prolong the full length of the sliding portion, thus posing a problem in that the whole pump becomes large in size.
Further, in the conventional high pressure fuel supply pumps described in Japanese Patent Application Laid-Open No. Hei 10-318068 and No. Hei 8-68370, since both ends of the seal material are made substantially at atmospheric pressure, it is necessary to provide, on the fuel chamber side of the seal material, a passage in communication with the fuel tank substantially at atmospheric pressure, thus making it necessary to have a passage for connecting the pump to the fuel tank. As a result, there was a problem in that processing of a pump becomes complicated, and a piping for connecting the pump to the tank is necessary, thus increasing the cost.
{circle around (3)} Next, with respect to the variable capacity mechanism, an apparatus heretofore known has the constitution wherein, for example, as described in Japanese Patent No. 2690734, an electromagnetic valve is provided within an intake passage, and a returning quantity to the intake side is controlled by opening and closing operation of the electromagnetic valve to thereby adjust the discharge quantity.
Further, the constitution is known for example, from Japanese Patent Application Laid-Open No. Hei 10-153157, wherein a check valve is provided within an intake passage, and a spill (overflow) valve is provided in a fuel spill (overflow) passage in communication with a pressurizing chamber whereby quantity of fuel spill to a fuel tank is controlled by opening and closing the spill valve to thereby adjust the discharge quantity.
Since rotation of a pump increases by a multiple of a cam of the pump with respect to the number of revolutions of the engine, it is necessary to open and close the intake valve or the spill valve in order of msec (millisecond). However, in such a state of high speed opening and closing, mass of the electromagnetic valve influences on the respondence.